Sims 3 had a solid base, packs filled with content and after 4 years, it was a completed and well-rounded game (IMO). Sims 4, on the other hand, still hasn't reached its full potential, even after 6 years, which is very disappointing, and missing features are being added dreadfully slowly. I do have to say that TS4 did improve on some things, but you would expect much more from the forth generation of the sims.
Also, I feel like with TS3, they would incorporate many ideas into one pack, but with TS4, one idea is often split into five different packs.